Fuel injection systems

ABSTRACT

An electronic fuel injection control includes a main fuel control circuit which operates to control fuel flow to the engine by controlling the duration of engine-synchronized fuel valve opening pulses in accordance with at least one engine parameter. An auxiliary pulse source is arranged to provide extra unsynchronized pulses to improve the acceleration characteristics of the control, such pulses being produced when the throttle is opened. A muting circuit is provided which operates for a fixed period following closing movement of the throttle, to prevent the auxiliary pulse source responding to throttle opening during said period. The muting circuit prevents excess fuelling during gear changes etc.

This is a continuation of application Ser. No. 847,625 filed Nov. 1, 1977, now abandoned.

This invention relates to an electronic fuel injection control for an internal combustional engine.

An electronic fuel injection control in accordance with the invention comprises a main fuel control circuit for applying to at least one fuel injection valve pulses of duration determined by at least one engine operating parameter controlling said main fuel control circuit, an auxiliary pulse source sensitive to opening movement of the engine throttle for applying at least one additional pulse to said fuel injection valve when the throttle is opening, and muting means sensitive to closing movement of the throttle and arranged to prevent the auxiliary pulse source from producing a pulse for a predetermined time following closing movement of the throttle.

The auxiliary pulse source may be responsive to the rate of change of the position of the throttle so as to produce a pulse whenever the rate of change exceeds a predetermined positive value. In that case the muting means may be arranged to be brought into operation when the rate of change is less than a predetermined negative value.

Alternatively the auxiliary pulse source may be arranged to be actuated during throttle opening movement at specific throttle positions, muting occurring following throttle closing movement through associated specific throttle positions.

In the accompanying drawings

FIG. 1 is a schematic diagram illustrating one example of an electronic fuel injection control in accordance with the invention;

FIG. 2 is a circuit diagram of a part of the control shown in FIG. 1;

FIG. 3 is the circuit diagram of a temperature transducer circuit and a temperature "window" circuit forming part of the control of FIG. 1;

FIG. 4 is the circuit diagram of a clock pulse generator forming part of the control of FIG. 1;

FIGS. 5, 6, 7 and 8 are fragmentary circuit diagrams illustrating four possible modifications to the circuit shown in FIG. 2;

FIG. 9 is a graph illustrating the relationship between the clock pulse generator output frequency and the engine water temperature achieved in the example of the invention shown in FIGS. 1 to 4; and

FIG. 10 is a circuit diagram illustrating another example of an electronic fuel injection control in accordance with the invention.

Referring firstly to FIG. 1 the overall system comprises a main digital fuel control 10 of known type utilizing digital computation techniques to produce a digital fuel demand signal in accordance with the value or values of one or more engine operating parameters selected from air intake mass flow, engine speed, air intake manifold pressure, air intake throttle position. Such parameter or parameters is or are measured by one or more transducers 11. The digital fuel demand signal is generated by means of a read only memory matrix incorporated in the control 10 which produces a multi-bit digital output signal in accordance with the value or values of digital signals addressing the matrix and derived from the transducer or transducers. The multi-bit digital signal may be used in either of two equivalent ways. Firstly, it may be transferred to a presettable counter which is then clocked to zero or it may be applied, if need be via a latch, to one input of a digital comparator whilst the output of a counter being clocked up from zero is applied to the other input of the comparator. In either case the digital signal is transformed to a pulse duration directly proportional to the digital signal and inversely proportional to the clock frequency. FIG. 1 shows a clock pulse-generator 12 which provides the clock pulses and a fuel injector control 13 which receives the pulse duration modulated signals from the main fuel control 10.

The control 13 has two output terminals to which the pulse modulated signals from the control 10 are alternately steered, each output stage of the control 13 including an open collector power transistor (not shown). These output stages are connected to two groups of solenoids 16 forming part of a bank of fuel injection valves.

FIG. 1 illustrates a number of arrangements by means of which the clock pulse frequency is varied, both as a function of engine water temperature and as a function of the rate of movement of an accelerator pedal 17. The pedal 17 is linked to the slider of a potentiometer 18, which slider is connected by a buffer input stage 19 to an operational amplifier differentiating circuit 20, via a capacitor C₂ (which forms a part of the differentiating circuit). The circuit has clamping feedback circuits 21 and 22 which operate respectively in acceleration and deceleration. A water temperature "window" circuit 23 which controls a sensitivity switch 24 through the intermediary of which the output of the differentiating circuit 20 is applied to the clock 12 and also controls a time law circuit 29 at the input to the differentiating circuit 20. The "window" circuit 23 receives an input from a temperature transducer circuit 25, which also provides an input to the clock 12.

FIG. 1 also shows an "extra pulse" circuit 26 which is triggered by the acceleration clamping circuit 21, but which is muted for a predetermined time after a deceleration has been demanded by an input from the deceleration clamping circuit 22. The circuit 26 has an open collector output stage connected by parallel diodes 27, 28 to the solenoids 16 as will be explained in more detail hereinafter.

Turning now to FIG. 2 the potentiometer 18 is connected in series with a diode D₁ between a regulated voltage supply rail 30 and an earth rail 31. The slider of the potentiometer 18 is connected via a resistor R₁ and a capacitor C₁ in series to the rail 31. The common point of the resistor R₁ and capacitor C₁ at which there appears a filtered d.c. signal corresponding to the position of the slider of the potentiometer 18 is connected both to a terminal E (see also FIG. 4) and to the base of a pnp transistor Q₁ connected as an emitter follower buffer with its collector grounded to rail 31 and its emitter connected by a resistor R₂ to the rail 30.

The emitter of the transistor is connected by a time-law switch circuit to one side of a capacitor C₂ which forms the input of the differentiating circuit 20. The time law switching circuit comprises two resistors R₃, R₄ is series between the emitter of the transistor Q₁ and the capacitor C₂ with the resistor R₃ of larger ohmic value bridged by the collector-emitter of an npn transistor Q₂ which has its base connected by a resistor R₅ to a terminal D, (see also FIG. 3). A diode D₂ has its anode connected to the common point of the resistor R₄ and the capacitor C₂ and its cathode connected to the emitter of the transistor Q₁.

The other side of the capacitor C₂ is connected by a resistor R₆ to the inverting input terminal of an operational amplifier A₁, the non-inverting input terminal of which is connected to the common point of two resistors R₇, R₈ connected in series between the rails 30, 31. Feedback around the amplifier A₁ is provided by the parallel combination of a resistor R₉ and a capacitor C₃. The main differentiating action of the amplifier is provided the capacitor C₂ and the resistor R₉ which dominate the transfer function of the amplifier for low frequency signals. The resistors R₆ and capacitor C₃ provide an integral action at high frequency to overcome the differential action so that the transfer function at high frequencies is integral rather than differential. This eliminates or at least substantially reduces the effect of high frequency noise and interference on the differentiating circuit.

The acceleration and deceleration clamping circuits share a common biasing chain R₁₀, R₁₁ and R₁₂ connected in series between the rails 30, 31. The common point of the resistors R₁₁ and R₁₂ is connected to the cathode of a diode D₃ with its anode connected to the base of an npn transistor Q₃ which has its collector connected to said other side of the capacitor C₂ and its emitter connected by a resistor R₁₃ to the emitter of pnp transistor Q₄ having its collector connected to the rail 31 by a resistor R₁₄. The base of the transistor Q₄ is connected by a resistor R₁₅ to the rail 31 and is also connected to the cathode of a diode D₄ which has its anode connected to the output terminal of the amplifier A₁.

The common point of the resistors R₁₀ and R₁₁ is connected by two diodes D₅, D₆ in series to the base of a pnp transistor Q₅, the collector of which is connected to said other side of the capacitor C₂. The emitter of the transistor Q₅ is connected by a resistor R₁₆ to the emitter of an npn transistor Q₆ the collector of which is connected by a resistor R₁₇ to the rail 30. The base of the transistor Q₆ is connected directly to the output terminal of the amplifier A₁.

The bases of the transistors Q₃, Q₅ are interconnected by a resistor R₁₈.

In steady state conditions the output terminal of the amplifier A₁ will be at at voltage set by the resistors R₇ and R₈. This will set the voltage at the base of the transistor Q₄ higher than the voltage at the base of the transistor Q₃ so that neither of these will conduct and similarly the transistors Q₅, Q₆ will be off.

During acceleration the output of the amplifier A₁ falls to a level determined by the rate of increase of the voltage at the slider of the potentiometer 18. Should this output voltage fall to a level lower than that at the junction fo the resistors R₁₁ and R₁₂, the transistors Q₃ and Q₄ will both turn on, diverting sufficient current from the capacitor C₂ to hold the amplifier output constant. When the increase in input voltage ceases capacitor C₂ can charge through the resistor R₄ and the transistor Q₂ (assuming this to be conductive) and the amplifier output returns to its previous voltage at a rate determined by such charging. If the transistor Q₂ is not conductive, the inclusion of the resistor R₃ is the charge path of the capacitor C₂ so as to delay the release of clamping and also increase the duration of charging.

In deceleration, the output of the amplifier A₁ increases and eventually turns on transistors Q₅ and Q₆ to provide the clamping action, when the voltage at the base of transistor Q₁ ceases to fall the capacitor C₂ discharges rapidly via the diode D₂ irrespectively of whether the transistor Q₂ is conductive or not.

The diodes D₃ and D₄ are included to compensate for the base-emitter voltages of the transistors Q₃ and Q₄ so that no temperature drift effects occur. Similarly the base-emitter voltages of the transistors Q₅ and Q₆ are compensated for by the diodes D₅ and D₆.

The output terminal of the amplifier A₁ is connected to the rail 30 by two resistors R₁₉, R₂₀ in series and to an output terminal A by a resistor R₂₁, pnp transistor Q₇ has its emitter connected to the common point of the resistors R₁₉ and R₂₀, its collector connected to the terminal A and its base connected by a resistor R₂₃ to the terminal D. The transistor Q₇ constitutes the sensitivity switch 24 of FIG. 1. As will be explained hereinafter the terminal A is held at a fixed voltage such that the amplifier A₁ draws current from terminal A via the resistor R₂₁. When transistor Q₇ is on the resistors R₁₉, R₂₀ are arranged to draw no current from terminal A when the signal output is steady, but the overall gain of the circuit is increased--i.e. the current drawn by the amplifier A₁ from the terminal A increases for a given rate of increase of the input signal from the accelerator pedal potentiometer 18.

FIG. 2 also shows the extra pulse circuit 26. This is constituted by a transistor Q₈ with its emitter grounded to the rail 31 and its collector connected by two resistors R₂₄, R₂₅ in series to the rail 30. The junction of the resistor R₂₄, R₂₅ is connected by two resistors R₂₆, R₂₇ in series to the rail 31 and by a resistor R₂₈ to the inverting input terminal of a voltage comparator A₂, a diode D₇ bridging the resistor R₂₈ and a capacitor C₄ connecting the collector of the transistor Q₈ to the inverting input terminal of the comparator A₂. The non-inverting input terminal of the comparator A₂ is connected by a resistor R₂₉ to the junction of the resistors R₂₆, R₂₇. The non-inverting input terminal is also connected by a resistor R₃₀ to a terminal C' (see FIG. 3). The output terminal of the comparator A₂ is connected by a resistor R₃₁ to the rail 30 and by two resistors R₃₂, R₃₃ in series to the rail 31. The common point of the resistors R₃₂, R₃₃ is connected to the base of a transistor Q₉, the emitter of which is grounded to the rail 31 and the collector of which is connected to the cathodes of the diodes 27, 28.

When the transistor Q₄ turns on as the acceleration clamping level is reached current flows in resistor R₁₄ flows until at some point the transistor Q₈ turns on. This reduces the voltage at the junction of the resistor R₂₄ and the capacitor C₄. Initially, however, capacitor C₄ draws current through the resistor R₂₈ and thus causes the output of the comparator A₂ to go high until the capacitor C₄ is charged to a given level. The transistor Q₉ conducts for the duration of this pulse, causing an additional injection action from all the injectors simultaneously. When the transistors Q₄ and Q₈ turn off again the diode D₇ allows rapid discharge of the capacitor C₄, and limits the voltage excursion of the inverting input terminal of the comparator A₂.

For muting the extra pulse circuit just described an npn transistor Q₁₀ has its emitter connected to the rail 31 and its collector connected to the non-inverting input terminal of the comparator A₂. The base of the transistor Q₁₀ is connected to the common point of two resistors R₃₄ and R₃₅ connected in series between the rail 31 and the collector of a pnp transistor Q₁₁. The base of Q₁₁ is connected to the collector of the transistor Q₆ and its emitter is connected to the rail 30. A capacitor C₅ is connected between the base and collector of the transistor Q₁₁.

When the transistor Q₆ turns on as the deceleration clamping level is reached, the transistor Q₁₁ turns on at a predetermined higher level set by the resistor R₁₇ thereby turning on transistor Q₁₀ and grounding the non-inverting input terminal of the comparator A₂. The transistor Q₁₁ does not turn off immediately the transistor Q₆ turns off because the capacitor C₅ continues to supply base current to the transistor Q₁₁ for a predetermined period, thereby preventing operation of the extra pulse circuit for a predetermined time after a "clamping level" deceleration has taken place. This muting arrangement comes into play when rapid pedal movements are executed such as during gear changing or during repeated acceleration of an unloaded engine prior to pulling away from rest.

The temperature dependent circuit of FIG. 3 includes a thermistor R₄₀ sensitive to the engine cooling water temperature. The thermistor R₄₀ is connected between the base of a pnp transistor Q₁₂ and the rail 31 in parallel with a resistor R₄₁, a resistor R₄₂ being connected between such base and the rail 30. The collector of the transistor Q₁₂ is connected to the rail 31 and its emitter is connected by a resistor R₄₃ to the rail 30 and is also connected to a terminal C and to the anode of a diode D₈ with its cathode connected by a resistor R₈₅ to the rail 31 and also connected to the terminal C'. The cathode of the diode D₈ is also connected via a resistor R₄₄ to the inverting input terminal of a voltage comparator A₃, a further resistor R₄₅ connecting this input terminal to the inverting input terminal of a further voltage comparator A₄. The non-inverting input terminals of the comparators A₃ and A₄ are connected to the common points of three resistors R₄₆, R₄₇ and R₄₈ connected in series between the rails 30 and 31 so that the non-inverting input terminal of the comparator A₃ is at a higher voltage than that of comparator A₄. Positive feedback resistors R₄₉, R₅₀ connect the output terminals of the two comparators A₃, A₄ to their non-inverting input terminals so as to provide a small amount of hysteresis to prevent spurious triggering of the comparator. The output terminal of the comparator A₃ is connected to the inverting input terminal of the comparator A₄ and a load resistor R₅₁ is connected between the rail 30 and the output terminal of the comparator A₄ which is connected to the terminal D.

The voltage at the terminal C falls substantially linearly over the normal working range of the system. At low temperatures (e.g. below 15° C.) the output of the comparator A₃ is low and that of the comparator A₄ is therefore high. As the temperature rises and the voltage at terminal C falls, the comparator A₃ switches so that the output of the comparator A₄ goes low. As the temperature continues to rise the comparator A₄ switches (at about 60° C.) and its output goes high again.

Turning now to FIG. 4, the clock pulse generator includes a pnp transistor Q₁₃ with its base at a fixed voltage (of about 3.3 V) and its collector connected by a capacitor C₆ to the rail 31. The emitter of the transistor Q₁₃ is connected by a resistor R₅₂ to the rail 30 and is also connected to the terminal A. The terminal C of FIG. 3 is also arranged to provide an input to the clock circuit to vary the proportion of the current in resistor R₅₂ which enters the emitter of the transistor Q₁₃. The terminal C is connected to the base of two npn transistors Q₁₇ and Q₁₈ which have their collectors connected to the emitter of the transistor Q₁₃. The emitter of the transistor Q₁₇ is connected to the common point of two resistors R₈₆ and R₈₇ connected in series between the rails 30, 31. Similarly the emitter of the transistor Q₁₅ is connected to the common point of two resistors R₈₈, R₈₉ connected in series between the rails 30, 31. The resistors R₈₆ to R₈₉ are chosen so that the transistor's Q₁₇, Q₁₈ switch off at different voltage levels of terminal C. Thus the current drawn by the transistors Q₁₇, Q₁₈ will decrease with increasing temperature, initially at a relatively steep slope until the transistor Q₁₇ turns off and then at a shallow slope until transistor Q₁₈ turns off. At higher temperatures the current drawn through the resistor R₅₂ is not temperature dependent. The collector of the transistor Q₁₃ is connected to the non-inverting input terminal of a comparator A₅ which has a load resistor R₅₄ connected between its output terminal and the rail 30. The inverting input terminal of the comparator A₅ is connected by a resistor to the common point of two resistors R₅₅, R₅₆ connected in series between the rails 30 and 31. The output terminal of the comparator A₅ is connected to the base of an npn transistor Q₁₄ the emitter of which is connected by a resistor R₅₈ to the rail 31 and the collector of which is connected to the inverting input terminal of the comparator A₅. A second non transistor Q₁₅ has its base connected to the emitter of the transistor Q₁₄, its emitter grounded to the rail 31 and its collector connected to the non-inverting input terminal of the comparator A₅. Because of the fixed voltage bias on the base of the transistor Q₁₃ its emitter is held at a fixed voltage (about 4 V) and the current passing through the resistor R₅₂ is constant. A very small amount of this current passes through the base-emitter junction of the transistor Q₁₃ and variable amounts are sunk via the terminal A and via the transistors Q₁₇ and Q₁₈ depending on the conditions in the FIG. 1 circuit and the temperature respectively. The remaining current passes into the capacitor C₆ charging it linearly whenever the transistor Q₁₅ is off. This occurs whenever the output of the comparator A₅ is low so that the voltage at the non-inverting input terminal of the comparator rises linearly until it exceeds the voltage set at the inverting input terminal. The output of the comparator A₅ now goes high turning on both transistors Q₁₄ and Q₁₅. The transistors Q₁₄ causes the voltage at the inverting input terminal to be reduced by drawing current through the resistors R₅₅ and R₅₇ , thereby increasing the speed of switching and the transistor Q₁₅ discharges the capacitor C₆, rapidly. The comparator A₅ then switches back to its original state and the cycle re-starts. For a fixed voltage at the junction of the resistors R₅₅, R₅₆ the frequency of the clock is proportional to the capacitor C₆ charging current.

The voltage at the junction of resistors R₅₅ and R₅₆ is not, however constant because of the effect of the components shown at the left hand side of FIG. 4. These components include a voltage comparator A₆ which has its non-inverting input terminal connected by a resistor R₆₀ to the terminal E (of FIG. 2) and its inverting input terminal connected to the common point of two resistors R₆₁, R₆₂ connected in series between the rail 31 and the cathode of a diode D₉ the anode of which is connected to the rail 30. The comparator A₆ has positive feedback from its output terminal to its non-inverting input terminal via a resistor R₆₃ and a further resistor R₆₄ connects the non-inverting input terminal to the rail 31. A resistor R₆₅ connects the output terminal of the comparator A₆ to the rail 30 and a resistor R₆₆ connects this output terminal to the junction of the resistors R₅₅ and R₅₆.

The comparator A₆ is set so that its output is normally low but goes high when the accelerator pedal is nearly fully depressed. This causes an increase in the voltage at the junction of the resistors R₅₅ and R₅₆ and therefore decreases the clock frequency and increases the quantity of fuel injected for a given fuel demand signal.

In addition two resistors R₆₇ and R₆₈ are connected in series between the rail 30 and the junction of the resistors R₅₅ and R₅₆. These normally increase the voltage at the junction of R₅₅ and R₅₆ slightly, but a terminal F at the junction of the resistors R₆₇ and R₆₈ is provided and can be grounded whenever it is intended that the vehicle in which the fuel injection control is installed is to be used predominatly at high attitudes. This increases the clock frequency and reduces the fuel injected.

Turning now to FIG. 9, the graph shows the overall effect of temperature on the clock frequency. The line A is the steady state frequency curve and the lines B and C show the limits of frequency variation resulting from clamping of the differentiating circuit in acceleration and deceleration respectively.

Below 15° C. and above 60° C. the transistor Q₇ is off because the output of the comparator A₄ which controls it is high. Relatively narrow limits of acceleration enrichment and deceleration enleanment are then permitted. In between 15° C. and 60° C. the output of the comparator A₄ goes low turning on the transistor Q₇ and the overall gain of the differentiator (considered as a current sink) increases.

In the modification shown in FIG. 5 gain variation with temperature is obtained by switching in and out an additional resistor R₇₀ in parallel with the resistor R₉. This is effected by means of an npn transistor Q₁₆ with its collector connected by the resistor R₇₀ to the inverting input terminal of the amplifier A₁ and its emitter connected to the output terminal of the amplifier A₁. A bias resistor R₇₁ is connected between the base and emitter of the transistor Q₁₆ to bias it off and a diode D₁₀ and a resistor R₆₉ in series connect the base of the transistor to the terminal D to turn the transistor Q₁₆ on at extreme temperatures and thereby reduce the gain of the differentiating circuit.

The modification shown in FIG. 6 affects the time law switch based on transistor Q₂. Instead of varying a resistance in series with the capacitor C₂, the transistor Q₂ now introduces a capacitor C₇ and resistor R₇₂ in series with one another across the capacitor C₂. This not only changes the time constants in the manner required but also varies the gain of the differentiator so that the transistor Q₇ of FIG. 2 can be omitted completely. The diode D₂ must also be emitted so that time law variations apply to acceleration and deceleration clamping.

The modification shown in FIG. 7 includes a quite different form of arrangement for varying the effect of the differentiation on the clock frequency with temperature. In this case the output of the amplifier A₁ is connected by a resistor R₇₃ to the common point of a pair of resistors R₇₄ and R₇₅ connected in series between the rails 30 and 31. The emitter of a transistor Q₁₇ is connected to this same common point, the collector of this transistor being connected to the terminal A and its base being connected by a resistor R₇₆ to the terminal C. This modification can be used in conjunction with the modifications shown in FIGS. 5 and 6 which give gain variation by alteration of feedback or by alteration of the input capacitance of the differentiating circuit.

Turning finally to FIG. 8 a different arrangement is shown for determining the clamping threshold levels. In this case separate potential dividers are used for biasing the acceleration and deceleration clamp circuits. The resistors R₈₀ and R₈₁ connected in series between the rails 30 and 31 have their common point connected to the cathode of the diode D₃. Two further resistors R₈₂ and R₈₃ connected in series between the rails 30, 31 have their common point connected to the anode of the diode D₅. The terminal D is connected to the cathode of a diode D₁₂ with its anode connected to the common point of the resistors R₈₀ and R₈₁ so that only the acceleration clamping threshold is altered when the signal at D goes low.

Turning now to FIG. 10 the invention is applied to a system which does not use the acceleration enrichment/deceleration enleanment of the example shown in FIGS. 1 to 4. Instead, an "extra pulse" circuit and corresponding muting circuit are used with an otherwise conventional system.

The main fuel control 110 controls the pulse lengths applied to injectors 116 (via diodes 114, 115) in accordance with signals from one or more engine parameter transducers 111. Diodes 117, 118 connect the solenoids to the "extra pulse" circuit.

This circuit includes an array of voltage comparators A₁₀₀, A₁₀₁ and A₁₀₂ which have their non-inverting input terminals connected by resistors R₁₀₀, R₁₀₁ and R₁₀₂ to different voltage points on a potential divider chain consisting of resistors R₁₀₃, R₁₀₄, R₁₀₅ and R₁₀₆ connected in series between a positive supply rail 130 and a ground rail 131. The inverting input terminals of the comparators A₁₀₀, A₁₀₁, and A₁₀₂ are connected by resistors R₁₀₇, R₁₀₈, and R₁₀₉ to one side of a capacitor C₁₀₀ the other side of which is grounded. Said one side of the capacitor C₁₀₀ is connected by a resistor R₁₁₀ to a potentiometer 120 operated by the accelerator pedal for the engine. Each comparator has positive feedback resistor R₁₁₁, R₁₁₂, R₁₁₃ to provide some hysteresis. Such hysteresis, used in combination with the filtering provided by the resistor R₁₁₀ and the capacitor C₁₀₀, prevents spurious triggering of the comparators A₁₀₀, A₁₀₁ and A₁₀₂ by noise and interference.

The output terminals of the comparators A₁₀₀, A₁₀₁ and A₁₀₂ are connected by resistors R₁₁₄, R₁₁₅, R₁₁₆ to a common point X which is connected by a resistor R₁₁₇ to the rail 130 (the comparators being of the open collector type). A capacitor C₁₀₁ couples to the point X to the base of an npn transistor Q₁₀₁ which base is also connected by a resistor R₁₁₈ to the rail 131.

A pnp transistor Q₁₀₂ is connected to act as a current source to provide current for charging the capacitor C₁₀₁. The emitter of the transistor Q₁₀₂ is connected by a resistor R₁₁₉ to the rail 130 and its base is connected to the common point of two resistors R₁₂₀, R₁₂₁ connected in series between the rails 130, 131, a thermistor R₁₂₂ (sensitive to engine water temperature) being connected in parallel with the resistor R₁₂₁. The collector of the transistor Q₁₀₂ is connected to the base of the transistor Q₁₀₁.

The collector of the transistor Q₁₀₁ is connected to the base of an npn output transistor Q₁₀₃ and also, by a resistor R₁₂₃ to the rail 130, both transistors Q₁₀₁ and Q₁₀₃ have their emitters connected to the rail 131 and the collector of the transistor Q₁₀₃ is connected to the cathodes of the diodes 117, 118.

In use the comparators A₁₀₀, A₁₀₁ and A₁₀₂ are switched sequentially as the slider of the potentiometer 120 is moved away from the grounded end of the potentiometer. Switching occur at three specific positions of the slider and each switching operation reduces the voltage at the point X. Transistor Q₁₀₁ is normally held on by the current from transistor Q₁₀₂ passing through the resistor R₁₁₈ and the base-emitter of the transistor Q₁₀₁. When the voltage at the point X falls, however the current from the transistor Q₁₀₂ is diverted to charge the capacitor C₁₀₁ and the transistor Q₁₀₁ turns off for time dependent on the charge in voltage at the point X and the current from transistor Q₁₀₂ (which varies with engine temperature). Transistor Q₁₀₃ is turned on for this same duration and causes extra pulses to be applied to the injector 116 in addition to the normal pulse duration modulated pulses from the main control circuit 10.

For muting the extra pulses immediately after deceleration, an npn transistor Q₁₀₄ is provided with its emitter connected to the rail 131 and its collector connected to the base of the transistor Q₁₀₁. The base of the transistor Q₁₀₄ is connected by a resistor R₁₂₄ to the cathode of a diode D₁₀₁ which is also connected by a capacitor C₁₀₂ to the rail 131. The anode of the diode D₁₀₁ is connected to the cathode of a diode D₁₀₂ with its anode connected to the rail 131. The anode of the diode D₁₀₁ is also connected by a capacitor C₁₀₃ and a resistor R₁₂₅ in series to the point X. The capacitors C₁₀₂, C₁₀₃ and the diodes D₁₀₁ D₁₀₂ constitute a diode pump circuit.

During deceleration the voltage at the point X goes up at three positions of the slider of the potentiometer 120. After each such increase in voltage at the point X the transistor Q₁₀₄ is turned on for a period determined by the voltage which is transferred to the capacitor C₁₀₂ through the diode D₁₀₁ and by the base current of the transistor Q₁₀₄. While transistor Q₁₀₄ is on transistor Q₁₀₃ cannot turn on.

It will be appreciated that rapid movement of the slider of potentiometer 120 will result in the comparators switching at very short intervals. During acceleration the effect is to produce a single extended pulse of duration approximately equal to the sum of the durations of the three pulses produced by slow movement of the slider. Similarly, rapid movement of the slider in deceleration causes the muting signal from transistor Q₁₀₄ to be extended. 

We claim:
 1. An electronic fuel injection control for an internal combustion engine having an engine throttle, the control comprising a main fuel control circuit for applying to at least one fuel injection valve pulses of duration determined by at least one engine operating parameter controlling said main fuel control circuit, an auxiliary pulse source sensitive to opening movement of the engine throttle for applying at least one additional pulse to said fuel injection valve when the throttle is opening, and muting means sensitive to closing movement of the throttle and arranged to prevent the auxiliary pulse source from producing a pulse for a predetermined time following closing movement of the throttle, said auxiliary pulse source comprising means sensitive to the rate of change of the position of the throttle so as to produce a pulse whenever the rate of change exceeds a predetermined positive value, said muting means being connected to said rate of change sensitive means so as to be brought into operation when the rate of change is less than a predetermined negative value.
 2. An electronic fuel injection control as claimed in claim 1 in which said rate of change sensitive means comprises a throttle position transducer producing an electrical signal dependent on the throttle position, and an operational amplifier differentiating circuit connected to said transducer.
 3. An electronic fuel injection control as claimed in claim 2 in which said differentiating circuiit incorporates two clamping means for clamping the operational amplifier output to limit levels representing limiting acceleration level and limiting deceleration level respectively, said auxiliary pulse source being connected to be operated by one clamping means and the muting means being connected to be operated by the other clamping means.
 4. An electronic fuel injection control for an internal combustion engine having an engine throttle, the control comprising a main fuel control circuit for applying to at least one fuel injection valve pulses of duration determined by at least one engine operating parameter controlling said main fuel control circuit, an auxiliary pulse source sensitive to opening movement of the engine throttle for applying at least one additional pulse to said fuel injection valve when the throttle is opening, and muting means sensitive to closing movement of the throttle and arranged to prevent the auxiliary pulse source from producing a pulse for a predetermined time following closing movement of the throttle, said axuiliary pulse source comprising a plurality of comparators connected to compare the output of a throttle position transducer with a plurality of reference signals, the auxiliary pulse source producing pulses when the throttle is moved in throttle opening direction through positions corresponding to said reference signals, said muting means being brought into operation when the throttle is moved in throttle closing diirection through positions corresponding to said reference signals.
 5. An electronic fuel injection control as claimed in claim 4 in which said auxiliary pulse source comprises a transistor switching circuit, a current source connected to said switching circuit to provide bias current thereto, a resistor network interconnecting the outputs of said comparators and a capacitor coupling said resistor network to the switching circuit so as to divert the bias current into the capacitor for a period following each switching action of each comparator during opening movement of the throttle.
 6. An electronic fuel injection control as claimed in claim 5 in which said muting means comprises a diode pump circuit connected to said resistor network and a transistor controlled by said diode pump circuit for disabling said switching circuit. 